Semiconductor memory devices are rapidly-accessible memory devices. In a semiconductor memory device, the time required for storing and retrieving information generally is independent of the physical location of the information within the memory device. Semiconductor memory devices typically store information in a large array of cells. A group of cells are electrically connected together by a bit line, or data line. An electrical signal is used to program a cell or cells.
Computer, communication and industrial applications are driving the demand for memory devices in a variety of electronic systems. One important form of semiconductor memory device includes a non-volatile memory made up of floating-gate memory cells called flash memory. Computer applications use flash memory to store BIOS firmware. Peripheral devices such as printers store fonts and forms on flash memory. Digital cellular and wireless applications consume large quantities of flash memory. Portable applications such as digital cameras, audio recorders, personal digital assistants (PDAs) and test equipment also use flash memory as a medium to store data.
To achieve increasing performance requirements and to lower power demands, components of the memory device have been scaled down in terms of size and operating voltages. Unless the voltage supplied to the memory device is matched to the operating voltages of the components, care must be taken to avoid failures or errors within the device.
Sensing a data value of a memory cell in a flash memory device often includes a precharging operation where the bit line containing the target memory cell is precharged to some precharge potential. This precharge is often the supply potential. It is important that this precharge potential achieved on the bit line not be of a magnitude that will cause a read disturb, i.e., a partial programming, of the memory cells when its word line is driven. Even small accumulations of charge on the floating gate of the flash memory cell may be accumulated over several sensing operations such as to alter the data value stored in the cell. For reliability of the memory device, it is thus extremely important to mitigate such read disturb effects.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative sensing devices for integrated-circuit memory devices, memory devices containing such sensing devices, and methods of their operation.